1. Field of the Invention
The present invention relates to a valve gear for an internal combustion engine, the device being provided with a function to make variable the valve operating characteristics of the opening and dosing of engine valves.
2. Description of Background Art
Valve gears are known for internal combustion engines is provided with a drive cam that rotates integrally with a camshaft supported by cylinder heads, a valve cam that is oscillably supported by the camshaft and opens and closes engine valves, a link mechanism that is oscillably supported centrally by the camshaft and transmits the valve driving force of the drive cam to the valve cam and oscillates the valve cam, a holder which, centering on a fulcrum provided on the link mechanism, can turn around the camshaft, and a driving mechanism that varies the fulcrum position of the link mechanism by turning this holder, and can make variable the valve operating characteristics of the engine valves according to the oscillating position of the oscillated link mechanism (See, for example, JP-A No. 2008-208800).
The known valve gear for internal combustion engines as disclosed in JP-A 2008-208800 involves a problem that the longitudinal length of the cylinder head is increased by the arrangement of a coil spring (a sub-rocker aim return spring), which presses the sub-rocker arm constituting the link mechanism against the drive cam, in the longitudinal direction of the vehicle. Further, as a compression coil spring (return spring) for the valve cam is provided between the holder and the valve cam for opening and closing the engine valves in a compressed state between the valve cam and the holder, the coil spring should be compressed when the holder is to be fitted, making the fitting work difficult.
Another known valve gear for internal combustion engines is disclosed in JP-A 2005-207255. It has a configuration in which the holder has a pair of plates inserted into the camshaft and so arranged as to hold the drive cam between them and the drive cam is pressure-fitted into and fixed in the camshaft, it is possible, in assembling the valve gear, to pressure-fit the drive cam after inserting one of the plates into the camshaft and then to insert the other plate into the camshaft. However, this configuration takes many man-hours to assemble because the drive cam formed as another element from the camshaft is to be pressure-fitted.